In wireless communication system, multifunctional circuit module is widely concerned because of its advantages such as small size and good overall performance. Antenna and filter are two indispensable elements at radio frequency front end. Generally, the antenna and the filter are individually designed as two elements, and then these two elements are matched to 50 ohm standard ports respectively, and subsequently cascaded. As such, the size of the entire module is increased, which is unfavorable to the radio frequency front end with a limited space. Since bandwidths of the filter and the antenna are not completely consistent, resulting in that the filtering performance is affected. To overcome these problems, a module where both the filter and the antenna are integrated is provided.
At present, most solutions of integrating filter and antenna choose co-design. In these solutions, the antenna and the filter are directly connected, and do not need to be matched to the 50 ohm standard port. Co-design reduces the size of the module and prevents loss caused by matching to the standard port. Although the co-design of the filter and the antenna improves the performance of the module to some extent, the loss of the filter is inevitable, especially in broadband design when a multi-order resonator is desired, the loss is more severe, and the antenna gain is relatively low.
Currently, few antenna designs can achieve good filtering performance and harmonic suppression function without using a complicated filtering circuit.